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June 13, 1967 Filed Feb. 7, 1965 c. D'A. HUNT ETAL 3,325,620

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l FURNACE 4 Sheets-Sheet 3 INVENTORS omai.; 114, #aA/7- fwd/l P, 5M/ ffm/e June 13, 1967 Filed Feb. '7 1965 June 13, 1967 c. DA. HUNT ETAL 3,325,620

FURNACE Filed Feb. 7, 1963 4 Sheets-Sheet 4 IN VENTORS l MMI d/M, Mz, a mf@ United States Patent O 3,325,620 FURNACE Charles DA. Hunt, Orinda, and Hugh R. Smith, Jr., Piedmont, Calif., assignors to-Temescal Metallurgical Corporation, Berkeley, Calif., a corporation of Califoi-nia Filed Feb. 7, 1963, Ser. No. 256,959 7 Claims. (Cl. 219-50) This invention relates generally to the continuous annealing of me-tallic strip material, and is particularly directed to a continuous strip lannealing method and apparatus wherein electron beam heating techniques in high vacuum are employed to heat the strip material to annealing temperatures.

Heretofore, continuous strip annealing has been conventionally accomplished with the aid of radiant type heating sources, such as extremely large and expensive gas iired furnaces. In 4order to insure that the strip material Will be heated to annealing temperatures in such radiant annealing unit-s, the strip must be moved therethrough in a large number of multi-pass slack loops. Substantial space must be provided in the annealing apparatus to accommodate the multi-pass slack loops. To provide uniformity of heating in the attainment of the annealing temperatures, the strip must be moved at constant speed inasmuch as rapid temperature control of radiant type heating sources to compensate for variations in strip speed is difficult, if not impossible, to obtain. In addition, radiant type annealers demand complicated start-up and shut-down procedures by virtue of the multipas-s slack loop and the inability of radiant heat sources to rapidly assume high operating temperatures or low shut-down temperatures. As a further disadvantage encountered in radiant type annealers, the strip must be thoroughly cleaned prior to the annealing operation.

An object of the present invention is the provision of a strip annealing method and apparatus which overcomes the above difficulties. Another object is the provision of a continuous strip annealing method and apparatus in which electron bombardment in high vacuum is utilized to heat the strip material to annealing temperatures. A further object is the provision of a con-tinuous strip annealing apparatus which is relatively inexpensive to construct and operate.

Other objects and advantages -of the present invention will become apparent from the following description and accompanying drawings, wherein:

FIGURE l is a side elevational view of a preferred embodiment of apparatus in accordance with the present invention, which may be advantageously employed in the conduct of the method thereof;

FIGURE 2 is a plan view of the apparatus of FIGURE 1.

FIGURE 3 is an enlarged cross-sectional view taken along line 3-3 of FIGURE 1, illustrating a typical dynamic strip seal of unique design which is advantageously employed in the apparatus;

FIGURE 4 is an enlarged cross-sectional view of the high vacuum chamber of the apparatus taken along line 4-4 of FIGURE l and showing the disposition of electron guns therein as arranged to heat the strip to high annealing temperatures by electron beam bombardment;

FIGURE 5 is an enlarged cross-sectional view of the cooling section of the apparatus taken along line 5-5 of FIGURE 1;

FIGURE 6 is a schematic diagram of the vacuum and cooling systems employed in the described embodiment;

FIGURE 7 is an enlarged elevational view, partially in section, of the dynamic strip seal illustrated in FIGURE 3 and depicting further structural details thereof;

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FIGURE 8 is a top view of the dyn-amic seal of FIG- URE 7; and

FIGURE 9 is a cross-sectional view of the seal taken along line 9-9 of FIGURE 8.

Considering now the present invention in some detail, particularly with reference to the method thereof, same generally includes the introduction of a -strip of metallic material into a high vacuum zone in which the strip is subjected to electron beam bombardment to heat same to annealing temperatures, and the subsequent cooling of the strip prior to removal of same to the atmosphere.

More particularly, a high vacuum zone, having an absolute pressure typically in the range of 10-3 to 1()-6 mm. of mercury, is first established ras by means of Vacuum pumps continuously evacuating an enclosed cham-ber. A strip of material to he annealed is continuously advanced through the high vacuum zone by a suitable conveyance system therein. As the strip passes through the high vacuum zone, it is continuously subjected to electron bombardment by one or more electron beams acting over a predetermined spatial area traversed by the strip. The strip, in bearing bombarded by the electrons, is heated to high temperatures very rapidly at rates determined by the energy and density characteristics `of the beam and the strip speed. The beam characteristics are such that the strip, in passing through the predetermined bombardment area at any strip speed, is Iheated to and maintained within an appropriate annealing temperature range for a suitable period of time necessary to complete the annealing process. In this regard, it will be appreciated that the beam of bombarding electrons as emitted, for example, from a suitable arr-ay of electron guns, may be very precisely and rapidly controlled as to energy and density, and hence as to the rate at which heating of the strip material proceeds. In order that `variations in strip speed over a wide range may be tolerated, without corresponding variations in strip heating, the beam energy and density characteristics are preferably controlled to produce heating rates in a suitable direct relation to strip speed productive of substantially constant temperatures within the annealing temperature range .for the strip material being processed. Thus, in accordance with the present invention, the strip speed need not be maintained constant during the annealing process.

In some instances, it is desirable to prolong the residence period during which the strip is held within annealing temperature range. Where such is the case, the heating due to electron bombardment may be supplemented by subjecting the strip to radiant heating following its traversal of the beam bombardment area. The amount of radiant heating employed is such as to make up radiant heat losses of the strip, and to thereby maintain the strip temperature attained from the electron bombardment heating for an extended period. Since the radiant heat losses are of relatively low order, employment of radiant heating to make up the losses is preferred over additional bombardment heating which would necessarily have to be conducted at impracticably low rates.

Following bombardment of the strip with electrons to heat and maintain the strip material in a predetermined annealing temperature range for a desired residence time, with or without supplemental radiant heating, the strip is cooled, as by advancing the heated portion thereof into heat exchange relation with a cooling medium. Where bright annealing is desired, the strip may be subjected to an inert gas atmosphere during cooling. Following cooling, the strip is discharged into the atmosphere.

The method of the invention described hereinbefore, may, of course, be employed to continuously anneal a variety of metallic strip materials. In one specific application, the method has been found useful for annealing 80,000 pounds per hour of 40-inch wide mild steel strip, rangmg from .007 to .0135 inch in thickness, at approximately 1400 degrees F. temperatures. In the specific application, the strip is continuously passed into a high vacuum zone in which the absolute pressure is reduced to within the range of 0.1 to 0.05 micron of mercury. The strip is continuously bombarded with electrons within the high vacuum zone over a 12 foot length of strip to raise and maintain the strip at a 1400 degree F. annealing temperature for a residence period of a few seconds. At this vacuum, the 1400 degrees F. temperature for the necessary residence period is attained with bombarding electrons at 8000 kw. of D.C. power and about 3000 cv. energy, evenly distributed over the aforementioned 12 foot length of strip and across the entire strip width. The strip is thereafter cooled to about 400 degrees F. in the presence or absence of an inert gas atmosphere prior to discharge into the atmosphere, depending upon whether or not bright annealing is desired.

Considering now a preferred embodiment of apparatus in which the method described hereinbefore may be advantageously conducted, reference is rst made to FIG- URES 1 and 2 wherein a continuous strip 1 of material to be annealed is fed into a vacuum vessel, referred to generally as 2. The vacuum vessel includes a series of entrance seal chambers 3a, 3b, and 3c, which are staged at progressively higher vacuums from atmospheric pressure to an absolute pressure within the range of about 0.1 to 0.05 micron of mercury, for example, which is maintained within a chamber 4 of the vacuum vessel to thereby define the high vacuum zone of previous mention. Well known power driven roll-type strip handling means 5 are provided at either end of vacuum vessel 2 to feed the strip therethrough.

In the illustrated embodiment, a plurality of electronic discharge devices or electron guns 6 are suitably supported, as by a horizontally disposed plate 7, above the strip 1 and within the high vacuum chamber 4. The guns 6 generate electrons for bombarding the continuously moving strip as it passes through the high vacuum zone to heat same to annealing temperatures, in accordance with the salient aspect of the present invention. Preferably the electron guns 6 are of the self accelerating type, such as that described in a pending application, Ser. No. 183,841, tiled Mar. 30, 1962, or the conventional Pierce type electron gun. The beam is preferably generated in a rectangular pattern rather than a circular pattern, to provide uniform strip heating.

Conventional work accelerated guns may also be employed in the apparatus, but generally are not as satisfactory for applications involving Wide strip. Irrespective of the type of electron gun employed, high voltage screens (not shown) may be advantageously disposed near the strip to assure high eiciency utilization of the beam by confining the beam to the strip.

As an example of one particular electron gun arrangement which may be employed in the apparatus, bombardment heating is accomplished in annealing the 80,000 pounds per hour of 40-inch wide mild steel strip of the example noted hereinbefore relative to the method, by electron beams of from 2,000 to 3,000 v. potential emanating from linear indirectly accelerated guns positioned about 2 feet above the strip. A total of sixteen guns arranged in four parallel rows of four guns each provide uniform heating across the full width of the 40-inch strip for a length of about 12 feet. Each row of four guns, eX- tending serially in the direction of strip travel, is connected to a common D.C. power supply and is controlled separately from each other row. The power supplies are advantageously extremely stable, high voltage D.C. units. For the foregoing example, eight power supplies rated at 1,000 kw. at 3,000 volts D.C. and capable of continuous current output of 333 amperes, provide power for the guns, a pair of power supplies for each row of guns.

The electron guns 6 are capable of being precisely controlled as to the characteristics of the electron beams emanating therefrom to the ends of heating the strip to within a predetermined annealing temperature range with rapidity, and maintaining the annealing temperature within close tolerances irrespective of variations in strip speed. The foregoing is advantageously accomplished in the apparatus 4of the present invention by means of a radiation pyrometer control system 8 (see FIGURE 6), coupled directly to the electron gun power supply to control annealing temperature within close tolerances. The control system, which may be of a conventional type, is arranged to responsively adjust power supply output to vary electron beam density and/or energy in predetermined relationship to the temperature of the strip, as sensed by a radiation pyrometer of the control system directly viewing the strip. In this connection, the control system automatically varies the beam energy and/or density in inverse relation to departures of the observed control temperature above and below a predetermined set annealing temperature. Inasmuch as the control temperature relates directly to strip speed, the control system operates to compensate for the effects of strip speed on strip temperature and the residence time of the strip at annealing temperature. Control systems of the type generally outlined above can be readily designed in accordance with common electronics practice to be capable of providing uniformity in annealing temperature across the strip of 15-50 degrees for temperatures Within the range of 1200-3200 degrees F., irrespective of strip speed variation.

In instances where it is desired to extend the residence period of the strip material within the annealing temperature range, as noted hereinbefore relative to the method of the invention, it is, of course, necessary to provide radiant heat sources, or the like, within the high vacuum chamber 4. In such instances, the radiant heat sources (not shown) are disposed within the high vacuum chamber 4 in a zone following the electron guns 6 in the direction of strip travel. The radiant sources are arranged to direct radiant heat energy upon the strip along a predetermined length of its travel, consonant with a predetermined prolonged residence time. The heating imparted to the strip in the radiant heat zone thus defined is only sufficient to supply radiant heat losses of the strip and to thus hold the strip temperature at the annealing value.

The moving strip, subsequent to heating, discharges from the high vacuum zone 4 onto the subsequent strip handling rolls 5 through a series of staged exit seal chambers, for example 9a, 9b, 9c, of the vacuum vessel 2, in which the pressure progressively increases to atmospheric. The strip resides within the exit seal chambers for so short a time that insignificant strip cooling takes place. Strip cooling is preferably done in an atmospheric cooling chamber 10 following exit seal chamber 9c. There closely spaced water-cooled heat transfer surfaces or chill plates 11 absorb heat radiated from the strip 1 as it passes between them. The plates, shown schematically in FIG- URE 5, are as close together as strip distortion and motion normal to the direction of travel permits. Coolant conduit 12 supplies circulating cooling water or other coolant to the plates. Air or inert gas circulated under forced convection between the strip 1 and chill plates 11, hastens strip cooling. Air is circulated in the event oxidation presents no problem or circulation of inert gas, such as argon or nitrogen provides bright annealing. Cool gas or air discharged from gas conduit means 13 circulates at high velocity between the closely spaced chill plates 11 and the strip 1. The high gas velocity significantly improves heat transfer from the strip. The length of the cooling zone depends upon system variables including strip speed, annealing temperature, and the final temperature desired. For instance, approximately G-1350 square free of transfer surface cools 40-ineh wide mild steel strip .007-.0135 inch thick traveling at 1,500 feet per minute from 1400 F. to 400 F. employing a coolant gas velocity of approximately 100 feet per second over the strip surfaces and cooling water temperatures of approximately 80 F.

Upon discharge from the cooling zone the strip continuously passes onto recoiling apparatus of a strip handling system, not a part of this invention, but which will be familiar to those skilled in this art. The strip moves straight through the annealing apparatus in a single pass with slack loops in the strip handling system only at each end of the annealing apparatus, instead of the multipass slack loops presently employed in radiant type annealers. The strip speed can be varied or the strip even stopped without danger of overheating. This insures the flexibility neede-d for quick starts and stops for maintenance, or for welding new rolls of strip or the like. This has not heretofore been possible.

A dynamic strip seal, one form of which is illustrated generally in FIGURE 3, and in detail in FIGURES 7-9, closes each end of the several entrance and exit seal chambers. These seals each comprise a pair of close clearance rolls 14a and 14b between which the moving strip passes. The lower roll 14a is rotatably mounted upon a fixed shaft 15 by means of radial bearings 16a. The ends of the shaft are fixedly retained in a pair of bearing blocks 17a suitably fastened to a housing 18. The illustrated housing 18 extends along the path of the strip 1 on either side of the nip of the rolls 14a and 14b and is provided with a passage 19 to permit the strip to pass therethrough. One end of the housing 18 is suitably fastened to a vertically extending wall 20 which is disposed between the several entrance and exit seal chambers. As shown particularly in FIGURE 9, apertures 21 and 22 are provided in the upper and lower wall of the housing 18 to permit the rolls 14a and 14b to engage the strip 1. The apertures 21 and 22 are of such a size and shape `as to effect a close clearance seal with the rolls 14n and 14b. The upper roll 14b is rotatably mounted on an eccentric shaft 23 by means of radial bearings 16b which shaft is oriented in parallelism with fixed shaft 15. The end portions of the eccentric shaft 23 are journalled in bearing .blocks 1711 by means of bearings 24. The bearing blocks 17 b are suitably joined to the housing 18. The pivot axis of the end portions of the eccentric shaft 23 is eccentric to the axis of rotation of upper roll 14b. This allows the upper roll 14b to pivot upwardly about the end portions of the shaft to afford passage of, for example, bumps in the strip 1 as it passes between the rolls. These bumps normally occur in the strip at joints where one length of strip is welded to another.

An eccentricity of about 5/32 inch between the pivot axis of the end portions and the rotational axis of the upper roll 14b is adequate for most applications using a four inch diameter roll. However, the eccentricity can be varied to accommodate a variety of strip distortions. The upper roll 14b pivots upwardly in opposition to turning moment exerted upon it by the differential pressure across the seal. In this connection, the housing 18 together with the rolls 14a and 14b are disposed on the higher pressure side of the wall 20. Thus, there is a higher pressure on the upper surface of the upper roll 14b than on the lower surface, whereby the upper roll 14b is biased downwardly against the moving strip 1. The pressure differential acting on the upper roll may be increased by exposing more of the lower surface of the upper roll to the lower pressure. In this connection, the upper wall of the housing extending between the upper roll and the wall 20 may be sp-aced further above the strip. Spring biasing means may be used to augment the downward bias developed by the pressure difference across the seal. This arrangement develops an extremely close clearance seal against the moving strip, regardless of strip thickness, and it minimizes air intrusion along the strip into the several seal chambers as Well as the high vacuum chamber itself. One of `the described dynamic seals is mounted at the end of each seal chamber, as appears schematically in FIGURE 6, to enclose the seal chambers as well as the high vacuum chamber between adjacent dynamic seals.

The dynamic seals between the high vacuum chamber 4 and exit seal chamber 9a and those between the several exit seal chambers are water cooled so that the hot strip may be handled without deterioration of the sealing elements. Water-cooling pipes 25 reduce exterior sur-face temperatures of the various vacuum vessel walls. The strip is easily re-threaded through the apparatus by provision of access doors 26 on each of the staged seal chambers and on the vacuum chamber 4.

FIGURE 6 schematically illustrates a vacuum system useful in reducing the pressure within the vacuum vessel 2. The system includes separate vacuum pump means for establishing staged vacuum levels in the several seal chambers 3a, 3b, 3c, and 9a, 9b, 9c, as well as for reducing the pressure in the high vacuum chamber 4 itself. For example, the pressure within the seal chamber 3a is reduced from atmospheric to about mm. of mercury by a backing pump 27 withdrawing air from the chamber through a conduit 28a and a block valve 29a. The pressure in seal chamber 3b is further reduced to about 9.5 mm. mercury by a backing pump 30 arranged in series with a secondary pump 31 to pump-down the chamber through a conduit 28h and block valve 29h. The entrance seal chamber 3c is drawn down to a pressure of 120 microns of mercury by a backing pump 32 and a secondary pump 33 connected to the chamber through a conduit 28e and a block valve 29C. Pressure switches 34 actuated by suction line pressure automatically start secondary pumps 31 and 33, upon attainment of a predetermined vacuum and simultaneously close bypass valves 35 provided around the secondary pumps.

A similar pumping arrangement on the exit seal chambers maintains the vacuum within exit seal chambers 9a, 9b, and 9c at pressures of 120 microns, 9.5 mm. and 85 mm. of mercury, respectively. A series connected backing pump 36 and a secondary pump 37 maintain the vacuum in the seal chamber 9a through an outlet conduit 38a and a block valve 39a. A backing pump 40 connected in series with a secondary pump 41 holds the vacuum in exit seal chamber 9b through an interconnecting conduit 3811 and a block valve 39b. A backing pump 42 taking suction through a line 38e and a block valve 39e` holds the vacuum in exit seal chamber 9c. Pressure switches 34 actuated by suction line pressure start the secondary pumps 37 and 41 upon the attainment of predetermined vacuums and simultaneously close the bypass valves 35. The backing pumps 40 and 42 on the last two exit seal chambers discharge directly through filter means 43 into a gas cooling system hereinafter described. Mechanical pumps generally are suitable for service as pumps 27, 30, 32, 36, 40 and 42 and Roots-type blowers, for pumps 31, 33, 37 and 41.

Three strip-jet type diffusion pumps 44, manifolded in parallel, draw-down and hold the pressure within the high vacuum chamber `4 at about `0.1 microns of mercury or less. Each pump is connected to the high vacuum chamber 4 by a pneumatic angle valve means 45 and each discharges through a lblock valve 46 into the remainder of the high vacuum system, including a secondary pump 47 `and a backing pump 48. On start-up the pumps 47 and 48 initially pump down the high vacuum chamber through a valved conduit 49 which -bypasses the diffusion pumps 44. Subsequently, the diffusion pumps 44 take over and draw down and hold the chamber at operating vacuum. The pressure switch 34 and the bypass valve 35 arrangement similar to that described on the seal chambers provides automatic start-up for the secondary pump 47.

The gas cooling system is also included as a portion of FIGURE 6, which for bright annealing includes an inert gas supply as at 50. Where oxidation is no problem air is useful as the coolant gas, `Control valve 51 actuated by a pressure controller 52 provides inert gas make-up to the cooling system. A compressor 53 circulates the cooling gas in the system and supplies gas under pressure through a flow meter 54 and valved conduit 13 to the surfaces of the chill plates 11. Gas from the cooling chamber 10 returns through valved conduit 55 to a cooler 56 and the suction of the compressor 53. The backing pumps 40 and 42 for the last two exit seal chambers 9b and 9c discharge into the return conduit 55 of the gas cooling system to return to the system any gas which may be lost through the dynamic seals into those chambers.

The described method and apparatus are useful for continuously annealing a wide variety of strip materials including stainless steel, titanium and other metals or even refractories. Extremely rapid and precise heating of the strip together with freedom from the restrictions of a constant strip speed provides the basis for a marked reduction in the total inventory of strip between the strip unwind and rewind stations. As a result, the described apparatus is considerably smaller than radiant annealers of equivalent throughput. This reduces initial capital costs and space requirements. Electron beam heating permits rapid start-up and shut-down procedures, since little time is required to produce a temperature swing between high annealing temperatures and low shut-down temperatures at which maintenance may be accomplished, new rolls of strip may be welded to the trailing end of `a strip undergoing annealing, or the like. In addition, heating of the strip by electron beam bombardment causes all oil or grease which may be present on the strip to vaporize without contamination of the strip surface. Finely divided solid particles on the strip surface have also lbeen observed to be removed to a large extent, apparently because of electrostatic effects. Consequently, the strip does not require cleaning prior to annealing.

Various modifications of the foregoing method and `apparatus will be apparent to those familiar with this art. The foregoing detailed description of a specific embodiment therefore has been given for clcarness of -understanding only and no unnecessary limitations should be understood therefrom. The invention is defined in the appended claims.

What is claimed is:

1. An apparatus for continuously annealing strip material Comprising, a vacuum vessel through which strip material to be annealed is passed in substantially nonlooped form, means for establishing a high vacuum within said vessel, means for feeding strip material through said vessel, said vessel including, in the direction of strip travel, a plurality of entrance seal chambers, a high vacuum chamber, a plurality of exit seal chambers, and a cooling chamber, said entrance and exit seal chambers being separated by dynamic roll seals, said entrance seal chambers being connected to a source of vacuum and adapted to be maintained at progressively higher vacuums in the direction of strip travel, said exit seal chambers `being connected to a source of vacuum and adapted to be maintained at progressively lower vacuums in the direction of strip travel, and a plurality of electron beam guns in said high vacuum chamber for heating the strip material to annealing temperature.

2. Apparatus in accordance with claim 1 wherein the cooling chamber includes opposed chill plates between which the strip passes, and means for cooling said chill plates.

3. Apparatus in accordance with claim 2 wherein means are provided for circulating air or inert gas over the strip during cooling.

4. Apparatus in accordance with claim 1 including a power supply for supplying power to the electron beam guns, and means for controlling the output of the power supply in response to the temperature of the heated strip.

5. Apparatus in accordance with claim 4 wherein said means is a radiation pyrometer.

6. Apparatus in accordance with claim 1 wherein the dynamic roll seals include a first roll rotatable about a fixed axis adapted to engage one surface of the strip and a second roll rotatable about a movable axis for engaging the opposite side of the strip, said second roll being rotatable about a second axis parallel to said fixed axis and shiftable toward and away from said fixed axis, and means for exposing a portion of the movable roll faced toward the strip to a lower pressure than a portion of the movable roll faced away from the strip.

7. A dynamic roll seal for transferring a continuous strip of material between two zones maintained at difierent pressures comprising a housing for encompassing the strip, a pair of rolls on said housing extending transversely of the strip on opposite sides thereof and rotatable in close clearance relation to said housing, one of said rolls being rotatable about a fixed axis, the other of said rolls being rotatable about a movable axis which axis is parallel to and shiftable with respect to said xed axis, and means for exposing the surface of said roll mounted on said movable axis facing the strip to a lower pressure than the surface of said roll facing away from the strip.

References Cited UNITED STATES PATENTS 2,585,277 2/1952 Seabold 266--3 2,654,587 10/ 1953 Skivesen 263-3 2,756,169 7/1956 Corson et al. 148--156 2,832,711 4/1958 Krahe et al. 148-156 2,929,614 3/1960 Young et al 34-242 X 2,932,502 4/1960 Rudd et al 266--3 3,020,032 2/1962 Casey 263-3 X 3,020,387 2/1962 Basche et al.

3,210,518 10/1965 Morley et al 219-121 JOSEPH V. TRUHE, Primary Examiner.

D. L. RECK, Examiner.

O. MARIAMA, Assistant Examiner. 

1. AN APPARATUS FOR CONTINUOUSLY ANNEALING STRIP MATERIAL COMPRISING, A VACUUM VESSEL THROUGH WHICH STRIP MATERIAL TO BE ANNEALED IS PASSED IN SUBSTANTIALLY NONLOOPED FORM, MEANS FOR ESTABLISHING A HIGH VACUUM WITH SAID VESSEL, MEANS FOR FEEDING STRIP MATERIAL THROUGH SAID VESSEL, SAID VESSEL INCLUDING, IN THE DIRECTION OF STRIP TRAVEL, A PLURALITY OF ENTRANCE SEAL CHAMBERS, A HIGH VACUUM CHAMBER, A PLURALITY OF EXIT SEAL CHAMBERS, AND A COOLING MEMBER, SAID ENTRANCE AND EXIT SEAL CHAMBERS BEING SEPARATED BY DYNAMIC ROLL SEALS, SAID ENTRANCE SEAL CHAMBERS BEING CONNECTED TO A SOURCE OF VACUUM AND 